1. Field of the Invention
The present invention relates to an optical transmission module. Particularly, the present invention relates to optical transmission module that can be reduced in size and weight and to which a multicore optical fiber ribbon or the like can be connected.
2. Description of the Related Art
Prior Art 1
When bi-directional communication is to be performed with a plurality of optical fibers, a system shown in FIG. 13 is constructed. This system is an optical fiber network in which optical fibers 330 are led into subscribers 320 from an optical communication equipment 310 provided in a central station 300. The optical communication equipment 310 is constituted of an assembly of a multitude of optical transmission modules 340.
One example of this optical transmission module is illustrated in FIG. 14. In this module 400, a light emitting device 420 or a light receiving device 430 is optically coupled to each core of the multicore optical fiber 330 via an FC type or SC type connector 410. More specifically, an optical fiber 440 connected to the connector 410, a lens 450, a mirror 460, a lens 470, and a light emitting device 420 such as a laser diode (LD) are coaxially arranged. On the other hand, a light receiving device 430 such as a photodiode (PD) is provided along the direction perpendicular to the axial direction of the optical fiber via a lens 480.
The multicore optical fiber ribbons 330 are led in up to the immediate forefront of this optical transmission module, and as shown in FIG. 15, the individual cores of the multicore optical fiber ribbons 330 are, after being separated, connected via connectors 410 to respective optical transmission modules arranged in parallel in the horizontal direction.
Prior Art 2
On the other hand, Japanese Unexamined Patent Application Publication No. 2000-200937 discloses a transmitter designated as a “parallel link” for optical parallel transmission. This is an optical parallel transmitter for optically coupling a plurality of light emitting devices and a plurality of optical fibers by positioning them with guide pins.
Prior Art 3
Also, Japanese Unexamined Patent Application Publication No. 11-237529 discloses an optical transmission/reception module that has transmission/reception functions by using a single optical fiber. This is an optical transceiver including a single light waveguide, a light emitting device, and a light receiving device. The waveguide and an external optical fiber are positioned with the guide pins, and are optically coupled.
However, the above-described prior arts raise a problem in that there is no appropriate compact means for collectively connecting multicore cores optical fibers to optical transmission modules.
In the optical transmission module according to the prior art 1, a multicore optical fiber ribbon cannot be connected to optical transmission modules unless it is branched out for every core. Therefore, the connector of each of the optical transmission modules must be arranged in parallel with some distance interposed between it and an adjacent connector. On the other hand, because the optical transmission module has an optical system in which the optical axis of the optical emitting device and that of the optical receiving device are orthogonal to each other, the manufacturing thereof is difficult, and the optical transmission module itself has a large size. Even if the parallel distance between the connectors is reduced, a large size of each of the optical transmission modules constitutes a large limiting factor on the miniaturization of this optical transmission module device.
In the prior art 2, a transmitter is the only one component that can be accommodated, and electronic components such as a driver Integrated Circuit (IC) of an LD cannot be mounted. This is because there is no space to mount a light emitting device since the parallel pitch of the optical fibers is as narrow as 250 μm.
The prior art 3 is a technique concerning a single optical fiber, and hence the technique is not capable of optically coupling multicores of optical fibers collectively to optical transmission modules.